Soft ferromagnetic mixed ferrite material



Aug. 3, 1954 v. c. WILSON 2,635,563

SOFT FERROMAGNETIC MIXED FERRITE MATERIAL I Filed May 10, l950 3 Sheets-Sheet l Pig F725.

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MDL PER CENT C00 mwaqmi gssb Patented Aug. 3, 1954 ATENT OFFICE SOFT FERROMAGNETIC MIXED FERRITE MATERIAL Volncy C. Wilson,

Schenectady, N. Y., assignor to General Electric Company, a. corporation of New York Application May 10, 1950, Serial No. 161,188

' 4 Claims. 1

The present invention relates to a soft ferromagnetic material consisting of mixed ferrites. It is particularly concerned with a mixed spineltype crystal ferrite characterized particularly by a low dielectric constant and a higt initial permeability combined with a high electrical resistivity.

Ferromagnetic oxides have been known for some time. All of them comprise one or more binary compounds of the formula MF204 (or MOFezOs) wherein M represents a bivalent metal. The fired or sintered ferrites or mixtures thereof are ordinarily in the form of mixed crystalline compounds, the magnetic properties of which depend to a large extent upon the particular metal or metals M employed in their preparation. For example the cobalt ferrites and cobalt nickel ferrites are hard (permanent) magnetic materials while mixed ferrites containing substantial amounts of examples of soft magnetic materials, 1. e., materials having a low coercive force.

Mixed Zinc ferrites includingthe nickel zinc ferrites are described in Snoek Patent 2,452,530

as comprising zinc ferrite having a low curiepoint combined with one or more cubic ferrites such as nickel ferrite of higher curie-point to obtain products having intermediate curie-points between 40 and 250 C. These mixed zinc ferrites are further described as having great chemical stability and hence a homogeneity on cooling favorable to good permeability, the latter value depending upon the particular proc ess employed in making the product, as for example, the number of times the material is resintered as well as the time of heating in an atmosphere of oxygen.

The present invention is based on the discovery that marked improvements in certain of the properties of the nickel zinc ferrites can be obtained by including small amounts of copper oxide as a fourth oxide constituent and maintaining the iron oxide content of the ferrite ma terial at a mol percentage slightly below 50 per cent.

More specifically it has been found that nickel zinc copper ferrites containing from 1 to 8 mol per cent, preferably from 2 to 6 mol per cent, copper oxide, from 4''! to 49 mol per cent ferric oxide, 28 to 38 per cent, preferably 28-32 percent, zinc oxide, balance nickel oxide are characterized by markedly improved permeabilities and higher A. C. and D. C. resistivities than comparable ferrites containing only nickel and zinc oxides in addition to the iron oxide. The ferrites of the zinc ferrite are 2 present invention are further noted for their high Q values and better over-all magnetic prop erties particularly at high frequencies. In addition, it has been found that these improved results are obtained without recourse to special firing conditions such as firing in an atmosphere of oxygen as recommended in the Snoek patent.

The invention and the advantages thereof will be more fully described with reference to the accompanying drawing in which the various figures show the properties of certain of the products of the present invention and the variation of certain of the properties of a nickel zinc ferrite material by including varying amounts of copper oxidefl i Fig. 1 shows the manner in which the resistivityvaries with change in the copper oxide content; Fig. 2 is a plotof the normal magnetization' curves of certain indicated compositions; Fig. 3 shows the effect of varying the firing temperature of a copper-free ferrite containing 59 mol per cent F6203, 20 mol per cent NiO and 30 mol per cent ZnO; and Figs. 4, 5 and 6 are plots of induction as a function of composition or (3110 content for 0.2, 1 and 60 oersteds respectively. I

The results plotted in Figs. 1, 2 and 4-6 were obtained on a series of ferrites prepared from 43 mol per cent F6203 and 30 mol per cent ZnO, but with various amounts of OuO and MO. As the CuO was increased, the amount of NiO was de creased keeping the sum of 'CuG plus NiO equal to 22 molar percent. In this series, samples were made with no CuO and with 1, 2, 3, 4, 5, 6, 8, 14, 17 and 20 mol per cent CuO. All the samples were fired at 1200 C. for 4 hours.

Fig. 1 shows the way the resistivity varies with percentage of CuO. From these results it will be seen that when a maximum resistivity substantially above 2 l0 ohm/cm. is desired, the ferrite should contain from 2 to 6, preferably 3 to 4 mol per cent CuO.

Normal magnetization curves were also taken for these samples. Fig. 2 shows some of these curves. To avoid confusion on the figure only about half of the samples are represented. With the addition of small amounts of CuO, both the permeability and. the maximum induction increases. This is very analogous to the increase obtained with a NiZn ferrite and no CuO- when firing to higher and higher temperatures as shown in Fig. 3 which is included for comparison. The material of Fig. 3 contained 50 mol per cent F6203, 20 mol per cent NiO, and 30 mol per cent ZnO fired 4 hours at the indicated temperatures. The composition is similar to that of this series with no CuO and it will be noted that the two normal magnetization curves at 1200 C. are nearly identical. The 2 per cent CuO- of this series compares with the formula of Fig. 3 fired at about 1300 C. Thus starting with a NiZn ferrite fired at 1200 C. the induction at all values of H is improved by either the addition of 2 per cent CuO or by increasing the firing temperature to 1300 C. Increasing the CuO to 8 per cent or increasing the firing temperature to 1390" C. increases the induction at H values below 1 oersted but decreases the induction above 1 oersted. Thus it is seen that one advantage of the addition of CuO to the NiZn ferrites is that for a given firing temperature, improved induction values can be obtained or conversely a desired induction value can be obtained at a lower firing temperature and hence at a lower processing cost. It would appear that within limits, the CuO additions effectively improve the formation of the desired spinel structure,

in Fig. 4 there is plotted induction values of the series of ferrites as a function of CuO content at 0.2 oersted. Fig. is a similar plot at 1 oersted and Fig. 6 at 60 oersteds. From these three figures it is apparent that in all cases the induction is improved by the addition of from 1 to 8 per cent CuO. The preferred amount to be added will depend upon the use to which the material is to be applied. If a field strength of 1 oersted is contemplated, then from 4 to 6 per cent CuO will give the highest induction and permeability. If the material is to be driven to higher H values, then about 2 per cent CuO will give the best results. If a high resistivity is required, then as shown by the results plotted in Fig. 1, from 3 to 4 per cent CuO should be used.

The dielectric constants of all of these materials were about the same; ranging from 15.5 to 24.1 in the frequency range from 0.6 to 5 me.

From these results, it is obvious that material and marked improvements in electrical resistivity and magnetic properties of the nickel zinc ferrites are obtained by substituting from 1 to 8 mol per cent, preferably 2 to 6 mol per cent, 0110 for the NiO content thereof. The proportions are critical as shown, for example, by the fact that the resistivity values drastically increase with the addition of a few per cent CuO and as quickly decrease when the CuO content materially exceeds 8 mol per cent.

The products of the present invention may be used for various core applications. Some of them, particularly those containing about 4 mol per cent CuO, have been found to be particularly useful in television sweep transformers.

A further advantage of the materials of the present invention is that these improved properties are obtained at relatively low firing temperatures in air. In other words, a special atmosphere such as an oxygen atmosphere is not required although it can be used if so desired. Also, while a firing or sintering temperature of 1200 C. is preferred, it is, of course, understood that the invention is not limited thereto. Higher or lower sintering temperatures can be employed with resultant variations in the properties of the sintered products in much the same way as was noted in connection with the straight nickel zinc ferrites of Fig. 3.

In general, as compared with the corresponding unmodified nickel zinc ferrite, the coppermodified materials give a higher permeability and combined with a higher resistivity, plus better performance characteristics particularly at frequencies of one megacycle and above.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A soft magnetic mixed crystal ferrite material consisting essentially of nickel ferrite, zinc ferrite and copper ferrite and having a metal oxide content of 47 to 49 mol per cent iron oxide, 1 to 8 mol per cent copper oxide, 28 to 38 mol per cent zinc oxide, balance nickel oxide, said mixed ferrite having a D. C. resistivity greater than 141) ohm-cm, and a magnetic induction greater than 400 gauss at a field strength of 1 oersted.

2. A soft magnetic mixed crystal ferrite material consisting essentially of nickel ferrite, zinc ferrite and copper ferrite and having a metal oxide content of 4'7 to 49 mol per cent iron oxide, 2 to 6 mol per cent copper oxide, 28 to 32 mol per cent zinc oxide, balance nickel oxide, said mixed ferrite having a D. C. resistivity of the order of 2 10 ohm-cm, and a magnetic induction greater than 1000 gauss at a field strength of 1 oersted.

3. A soft magnetic mixed crystal ferrite material consisting essentially of nickel ferrite, zinc ferrite and copper ferrite and having a metal oxide content of 47 to 49 mol per cent iron oxide, about 4 mol per cent copper oxide, 28 to 32 mol per cent zinc oxide, balance nickel oxide, said mixed ferrite having a D. C. resistivity of the order of at least 1x10 ohm-cm, and a magnetic induction greater than 1200 gauss at a field strength of 1 oersted.

4. A magnetic mixed crystal ferrite material consisting essentially of nickel ferrite, zinc ferrite and copper ferrite and having a metal oxide content of about 4 mol per cent copper oxide, about 28 mol per cent zinc oxide, about 18 mol per cent nickel oxide and slightly less than 50 mol per cent iron oxide.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,976,230 Kato et a1. Oct. 9, 1934 OTHER REFERENCES New Developments in Ferromagnetic Materials, Snoek, Elsevier Publishing Co., New York, 1947. 

1. A SOFT MAGNETIC MIXED CRYSTAL FERRITE MATERIAL CONSISTING ESSENTIALLY OF NICKEL FERRITE, ZINC FERRITE AND COPPER FERRITE AND HAVING A METAL OXIDE CONTENT OF 47 TO 49 MOL PER CENT IRON OXIDE. 1 TO 8 MOL PER CENT COPPER OXIDE, 28 TO 38 MOL PER CENT ZINC OXIDE, BALANCE NICKEL OXIDE, SAID MIXED FERRITE HAVING A D. C. RESISTIVITY GREATER THAN 107 OHM-CM, AND A MAGNETIC INDUCTION GREATER THAN 400 GAUSS AT A FIELD STRENGTH OF 1 OERSTED. 